Riner was born on 7 April 1989 in Les Abymes near Pointe-à-Pitre, in Guadeloupe an insular region of France in the Caribbean. He was raised in Paris. He was enrolled at a local sports club by his parents and played football, tennis and basketball, but says he preferred judo “because it is an individual sport and it’s me, only me.”

Riner was a member of the Levallois Sporting Club in Levallois-Perret, France and is coached by Christian Chaumont and Benoît Campargue. He won the World and European junior titles in 2006. In 2007, he won a gold medal at the European Judo Championships in Belgrade, Serbia, on the day after his eighteenth birthday. At the 2007 World Judo Championships in Rio de Janeiro, Brazil, he became the youngest ever senior world champion when he won the heavyweight (+100 kg) event, defeating the 2000 Olympic gold medallist, Kosei Inoue of Japan, in the semi-final.

In his career, Riner was only defeated eight times in elite international championships. He lost to Brayson and Tölzer in 2006, to Bianchessi and Rybak in 2007 and to Muneta and Grim Vuijsters in 2008. He lost to Abdullo Tangriev in the third round of the 2008 Summer Olympics, before obtaining the bronze medal, and on 13 September 2010 he lost the openweight title at the 2010 World Judo Championships in Tokyo to Daiki Kamikawa, his last defeat before a series of 154 victories. After almost 10 years, he lost in the third round of the Paris Grand Slam against world number 2 Kokoro Kageura.

At the 2008 Summer Olympics in Beijing, China, Riner competed in the men’s heavyweight event. He received a bye into the second round of the competition before beating Anis Chedli of Tunisia and Kazakhstan’s Yeldos Ikhsangaliyev to advance to the semi-finals. In the semis he was beaten by Uzbek judoka Abdullo Tangriev on the golden score, meaning Riner had to enter the repechage rounds. In the repechage he defeated Andreas Tölzer and João Schlittler to reach a bronze medal final against Lasha Gujejiani of Georgia; Riner took the bronze medal by a score of one ippon, one yuko and one koka to nil. In December 2008 he won his second World Championship gold medal at the Open weight Championships held in Levallois-Perret, France, by beating Alexander Mikhaylin of Russia in the final.

In 2010, he won two medals, a gold and a silver, at the World Championships in Tokyo. After winning the +100 competition Riner was defeated by Daiki Kamikawa of Japan in the final of open weight class by a 2–1 judge’s decision. After the bout, Riner refused to bow or to shake Kamikawa’s hand, claiming that he “was robbed”.

At the 2016 Olympics, he defended his Olympics heavyweight title, defeating Hisayoshi Harasawa in the final.